U.S. patent number 6,174,001 [Application Number 09/044,707] was granted by the patent office on 2001-01-16 for two-step, low torque wedge thread for tubular connector.
This patent grant is currently assigned to Hydril Company. Invention is credited to Doug Enderle.
United States Patent |
6,174,001 |
Enderle |
January 16, 2001 |
Two-step, low torque wedge thread for tubular connector
Abstract
A threaded pipe connection is disclosed that includes a box
member and a pin member. The box member has two wedge thread steps
each with a tapered, internal, generally dovetail-shaped wedge
thread having stab flanks, load flanks, roots, and crests. The pin
member has two wedge thread steps each with a tapered, external,
generally dovetail-shaped wedge thread having stab flanks, load
flanks, roots, and crests. The internal thread of the box member
increases in width in one direction. The external thread of the pin
member increases in width in the other direction so that
complementary flanks of the box member thread move into engagement
during rotational make-up of the connection. The roots and crests
of at least one wedge thread step on the box member are dimensioned
to contact complementary roots and crests on the pin member upon
final make-up. Also, stab and load flanks of at least one wedge
thread step on the box member are dimensioned to contact
complementary stab and load flanks on the pin member upon final
make-up.
Inventors: |
Enderle; Doug (Humble, TX) |
Assignee: |
Hydril Company (Houston,
TX)
|
Family
ID: |
21933878 |
Appl.
No.: |
09/044,707 |
Filed: |
March 19, 1998 |
Current U.S.
Class: |
285/334;
29/456 |
Current CPC
Class: |
E21B
17/0423 (20130101); F16L 15/002 (20130101); Y10T
29/49881 (20150115) |
Current International
Class: |
E21B
17/042 (20060101); E21B 17/02 (20060101); F16L
15/00 (20060101); F16L 15/06 (20060101); F16L
025/00 () |
Field of
Search: |
;285/333,114,334,355,390
;29/456 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Browne; Lynne H.
Assistant Examiner: Binda; Greg
Attorney, Agent or Firm: Rosenthal & Osha L.L.P.
Claims
What is claimed is:
1. A threaded pipe connection comprising:
a box member having a two-step wedge thread configuration
comprising two wedge thread steps each with a tapered, internal,
generally dovetail-shaped wedge thread having stab flanks, load
flanks, roots, and crests, the internal thread increasing in width
in one direction:
a pin member having a two-step wedge thread configuration
comprising two thread steps each with a tapered, external,
generally dovetail-shaped wedge thread having stab flanks, load
flanks, roots, and crests, the external thread increasing in width
in the other direction so that complementary flanks of the box
member thread move into engagement during rotational make-up of the
connection;
the roots and crests of at least one wedge thread step on the box
member are dimensioned to contact complementary roots and crests on
the pin member upon final make-up;
on the wedge thread step on the box member having roots and crests
dimensioned to contact complementary roots and crests on the pin
member, the stab and load flanks on the box member are dimensioned
to contact complementary stab and load flanks on the pin member
upon final make-up; and
at least one of the stab and load flanks of the other wedge thread
step on the box member are dimensioned to remain in clearance from
the corresponding stab and load flanks of the other wedge thread
step on the pin member upon final make-up.
wherein clearance exists between the load flanks of the other of
the wedge thread steps upon final makeup.
2. The connection of claim 1 wherein a clearance between the roots
and crests of the other of the wedge thread steps upon final
make-up.
3. A threaded pipe connection comprising:
a box member having a two-step wedge thread configuration
comprising two wedge thread steps each with a tapered, internal,
generally dovetail-shaped wedge thread having stab flanks, load
flanks, roots, and crests, the internal thread increasing in width
in one direction;
a pin member having a two-step wedge thread configuration
comprising two thread steps each with a tapered, external,
generally dovetail-shaped wedge thread having stab flanks, load
flanks, roots, and crests, the external thread increasing in width
in the other direction so that complementary flanks of the box
member thread move into engagement during rotational make-up of the
connection;
the roots and crests of at least one wedge thread step on the box
member are dimensioned to contact complementary roots and crests on
the pin member upon final make-up;
on the wedge thread step on the box member having roots and crests
dimensioned to contact complementary roots and crests on the pin
member, the stab and load flanks on the box member are dimensioned
to contact complementary stab and load flanks on the pin member
upon final make-up; and
at least one of the stab and load flanks of the other wedge thread
step on the box member are dimensioned to remain in clearance from
the corresponding stab and load flanks of the other wedge thread
step on the pin member upon final make-up,
wherein clearance exists between the roots and crests of the other
of the wedge thread steps upon final make-up.
4. A threaded pipe connection comprising:
a box member having a two-step wedge thread configuration
comprising two wedge thread steps each with a tapered, internal,
generally dovetail-shaped wedge thread having stab flanks, load
flanks, roots, and crests, the internal thread increasing in width
in one direction;
a pin member having a two-step wedge thread configuration
comprising two thread steps each with a tapered, external,
generally dovetail-shaped wedge thread having stab flanks, load
flanks, roots, and crests, the external thread increasing in width
in the other direction so that complementary flanks of the box
member thread move into engagement during rotational make-up of the
connection;
the roots and crests of at least one wedge thread step on the box
member are dimensioned to contact complementary roots and crests on
the pin member upon final make-up;
on the wedge thread step on the box member having roots and crests
dimensioned to contact complementary roots and crests on the pin
member, the stab and load flanks on the box member are dimensioned
to contact complementary stab and load flanks on the pin member
upon final make-up; and
at least one of the stab and load flanks of the other wedge thread
step on the box member are dimensioned to remain in clearance from
the corresponding stab and load flanks of the other wedge thread
step on the pin member upon final make-up,
wherein clearance exists between the stab flanks of the other of
the wedge thread steps upon final make-up, and clearance exists
between the roots and crests of the other of the wedge thread steps
upon final make-up.
5. A threaded pipe connection comprising:
a box member having a two-step wedge thread configuration
comprising two wedge thread steps each with a tapered, internal,
generally dovetail-shaped wedge thread having stab flanks, load
flanks, roots, and crests, the internal thread increasing in width
in one direction;
a pin member having a two-step wedge thread configuration
comprising two thread steps each with a tapered, external,
generally dovetail-shaped wedge thread having stab flanks, load
flanks, roots, and crests, the external thread increasing in width
in the other direction so that complementary flanks of the box
member thread move into engagement during rotational make-up of the
connection:
the roots and crests of at least one wedge thread step on the box
member are dimensioned to contact complementary roots and crests on
the pin member upon final make-up;
on the wedge thread step on the box member having roots and crests
dimensioned to contact complementary roots and crests on the pin
member, the stab and load flanks on the box member are dimensioned
to contact complementary stab and load flanks on the pin member
upon final make-up; and
at least one of the stab and load flanks of the other wedge thread
step on the box member are dimensioned to remain in clearance from
the corresponding stab and load flanks of the other wedge thread
step on the pin member upon final make-up,
wherein clearance exists between the stab flanks and the load
flanks of the other of the wedge thread steps upon final make-up,
and clearance exists between the roots and crests of the other of
the wedge thread steps upon final make-up.
6. A threaded pipe connection comprising:
a box member having a two-step wedge thread configuration
comprising two wedge thread steps each with a tapered, internal,
generally dovetail-shaped wedge thread having stab flanks, load
flanks, roots, and crests, the internal thread increasing in width
in one direction;
a pin member having a two-step wedge thread configuration
comprising two thread steps each with a tapered, external,
generally dovetail-shaped wedge thread having stab flanks, load
flanks, roots, and crests, the external thread increasing in width
in the other direction so that complementary flanks of the box
member thread move into engagement during rotational make-up of the
connection;
the roots and crests of at least one wedge thread step on the box
member are dimensioned to contact complementary roots and crests on
the pin member upon final make-up;
on the wedge thread step on the box member having roots and crests
dimensioned to contact complementary roots and crests on the pin
member, the stab and load flanks on the box member are dimensioned
to contact complementary stab and load flanks on the pin member
upon final make-up; and
at least one of the stab and load flanks of the other wedge thread
step on the box member are dimensioned to remain in clearance from
the corresponding stab and load flanks of the other wedge thread
step on the pin member upon final make-up,
wherein one of the wedge thread steps is an interference wedge
thread step and the other is a clearance wedge thread step; and
root and crest interference exists on the interference wedge thread
step and root and crest clearance exists on the clearance wedge
thread step upon final make-up.
7. A method of reducing torque-induced stress in a threaded pipe
connection, the method comprising:
providing a box member having a two-step wedge thread configuration
comprising two wedge thread steps each with a tapered, internal,
generally dovetail-shaped wedge thread having stab flanks, load
flanks, roots, and crests, the internal thread increasing in width
in one direction;
providing a pin member having a two-step wedge thread configuration
comprising two thread steps each with a tapered, external,
generally dovetail-shaped wedge thread having stab flanks, load
flanks, roots, and crests, the external thread increasing in width
in the other direction so that complementary flanks of the box
member thread move into engagement during rotational make-up of the
connection;
dimensioning the roots and crests of at least one wedge thread step
on the box member to contact complementary roots and crests on the
pin member upon final make-up;
dimensioning, on the wedge thread step on the box member having
roots and crests dimensioned to contact complementary roots and
crests on the pin member, the stab and load flanks on the box
member to contact complementary stab and load flanks on the pin
member upon final make-up; and
dimensioning at least one of the stab and load flanks of the other
wedge thread step on the box member to remain in clearance from
complementary stab and load flanks of the other wedge thread step
on the pin member upon final make-up,
wherein the load flanks of the other wedge thread step on the box
member are dimensioned to remain in clearance from complementary
load flanks on the pin member upon final make-up.
8. The method of claim 7, further comprising:
dimensioning the roots and crests of the other wedge thread step of
the box member such that clearance exists between complementary
roots and crests on the pin member upon final make-up.
9. A method of reducing torque-induced stress in a threaded pipe
connection, the method comprising:
providing a box member having a two-step wedge thread configuration
comprising two wedge thread steps each with a tapered, internal,
generally dovetail-shaped wedge thread having stab flanks, load
flanks, roots, and crests, the internal thread increasing in width
in one direction;
providing a pin member having a two-step wedge thread configuration
comprising two thread steps each with a tapered, external,
generally dovetail-shaped wedge thread having stab flanks, load
flanks, roots, and crests, the external thread increasing in width
in the other direction so that complementary flanks of the box
member thread move into engagement during rotational make-up of the
connection;
dimensioning the roots and crests of at least one wedge thread step
on the box member to contact complementary roots and crests on the
pin member upon final make-up;
dimensioning, on the wedge thread step on the box member having
roots and crests dimensioned to contact complementary roots and
crests on the pin member, the stab and load flanks on the box
member to contact complementary stab and load flanks on the pin
member upon final make-up;
dimensioning at least one of the stab and load flanks of the other
wedge thread step on the box member to remain in clearance from
complementary stab and load flanks of the other wedge thread step
on the pin member upon final make-up; and
dimensioning the roots and crests of the other wedge thread step of
the box member such that clearance exists between complementary
roots and crests on the pin member upon final make-up.
10. A method of reducing torque-induced stress in a threaded pipe
connection, the method comprising:
providing a box member having a two-step wedge thread configuration
comprising two wedge thread steps each with a tapered, internal,
generally dovetail-shaped wedge thread having stab flanks, load
flanks, roots, and crests, the internal thread increasing in width
in one direction;
providing a pin member having a two-step wedge thread configuration
comprising two thread steps each with a tapered, external,
generally dovetail-shaped wedge thread having stab flanks, load
flanks, roots, and crests, the external thread increasing in width
in the other direction so that complementary flanks of the box
member thread move into engagement during rotational make-up of the
connection;
dimensioning the roots and crests of at least one wedge thread step
on the box member to contact complementary roots and crests on the
pin member upon final make-up;
dimensioning, on the wedge thread step on the box member having
roots and crests dimensioned to contact complementary roots and
crests on the pin member, the stab and load flanks on the box
member to contact complementary stab and load flanks on the pin
member upon final make-up;
dimensioning at least one of the stab and load flanks of the other
wedge thread step on the box member to remain in clearance from
complementary stab and load flanks of the other wedge thread step
on the pin member upon final make-up;
wherein the stab flanks of the other wedge thread step on the box
member are dimensioned to remain in clearance from complementary
stab flanks on the pin member upon final make-up; and
dimensioning the roots and crests of the other wedge thread step of
the box member such that clearance exists between complementary
roots and crests on the pin member upon final make-up.
11. A method of reducing torque-induced stress in a threaded pipe
connection, the method comprising:
providing a box member having a two-step wedge thread configuration
comprising two wedge thread steps each with a tapered, internal,
generally dovetail-shaped wedge thread having stab flanks, load
flanks, roots, and crests, the internal thread increasing in width
in one direction;
providing a pin member having a two-step wedge thread configuration
comprising two thread steps each with a tapered, external,
generally dovetail-shaped wedge thread having stab flanks, load
flanks, roots, and crests, the external thread increasing in width
in the other direction so that complementary flanks of the box
member thread move into engagement during rotational make-up of the
connection;
dimensioning the roots and crests of at least one wedge thread step
on the box member to contact complementary roots and crests on the
pin member upon final make-up;
dimensioning, on the wedge thread step on the box member having
roots and crests dimensioned to contact complementary roots and
crests on the pin member, the stab and load flanks on the box
member to contact complementary stab and load flanks on the pin
member upon final make-up;
dimensioning at least one of the stab and load flanks of the other
wedge thread step on the box member to remain in clearance from
complementary stab and load flanks of the other wedge thread step
on the pin member upon final make-up,
wherein the stab and load flanks of the other wedge thread step of
the box member are dimensioned to remain in clearance from
complementary stab and load flanks on the pin member upon final
make-up; and
dimensioning the roots and crests of the other wedge thread step of
the box member such that clearance exists between complementary
roots and crests on the pin member upon final make-up.
12. A method of reducing torque-induced stress in a threaded pipe
connection, the method comprising:
providing a box member having a two-step wedge thread configuration
comprising two wedge thread steps each with a tapered, internal,
generally dovetail-shaped wedge thread having stab flanks, load
flanks, roots, and crests, the internal thread increasing in width
in one direction;
providing a pin member having a two-step wedge thread configuration
comprising two thread steps each with a tapered, external,
generally dovetail-shaped wedge thread having stab flanks, load
flanks, roots, and crests, the external thread increasing in width
in the other direction so that complementary flanks of the box
member thread move into engagement during rotational make-up of the
connection;
dimensioning the roots and crests of at least one wedge thread step
on the box member to contact complementary roots and crests on the
pin member upon final make-up;
dimensioning, on the wedge thread step on the box member having
roots and crests dimensioned to contact complementary roots and
crests on the pin member, the stab and load flanks on the box
member to contact complementary stab and load flanks on the pin
member upon final make-up;
dimensioning at least one of the stab and load flanks of the other
wedge thread step on the box member to remain in clearance from
complementary stab and load flanks of the other wedge thread step
on the pin member upon final make-up,
wherein one of the wedge thread steps is an interference wedge
thread step and the other is a clearance wedge thread step;
dimensioning the interference wedge thread step such that root and
crest interference exists upon final make-up; and
dimensioning the clearance wedge thread step such that root and
crest clearance exists upon final make-up.
Description
FIELD OF THE INVENTION
The invention relates to threaded tubular joints usable in oil and
gas well drilling and production, such as tubing, casing, line
pipe, and drill pipe, commonly known collectively as oilfield
tubular goods. More particularly, the invention relates to a
tubular joint for connecting male (pin) and female (box) members
without having to apply tremendous torque for make-up.
BACKGROUND OF THE INVENTION
The use of threaded tubular connections for joining flow conduits
in an end-to-end relationship to form a continuous flow path for
transporting fluid under pressure is well known. Oilfield tubular
goods all use threaded connections for connecting adjacent sections
of conduit or pipe. Examples of such threaded end connections
designed for use on oilfield tubular goods are disclosed in U.S.
Pat. Nos. 2,239,942; 2,992,019; 3,359,013; RE 30,647; and RE
34,467, all of which are assigned to the assignee of the present
invention.
In U.S. Pat. No. RE 30,647 by Blose, a particular thread form or
structure is disclosed for a tubular connection that provides an
unusually strong joint while controlling the stress and strain in
connected pin and box members within acceptable levels. The pin
member is equipped with at least one generally dovetail-shaped
external thread whose width increases in one direction along the
pin, while the box member is equipped with at least one matching
generally dovetail-shaped internal thread whose width increases in
the other direction. In this manner, the mating set of helical
threads provide a wedge-like engagement of opposing pin and box
flanks that limit the extent of relative rotation between the pin
and box members, and define a forcible make-up condition that
completes the connection. In this thread structure, the flank
shoulder angles as well as the thread width can be used to control
the stress and strain preload conditions induced in the pin and box
members for a given make-up torque. Thus, by tailoring the thread
structure to a particular application or use, the tubular
connection or joint is limited only by the properties of the
materials selected.
The wedge thread has been proven to be a reliable sealing mechanism
in threaded connections. The dovetail, wedging action of the
threads create sufficient interference in roots, crests, load
flanks, and stab flanks to effect the thread seal. The friction
drag caused by the interference threads must be overcome with
torque during the make-up process. The larger the area of thread
interference, the greater the torque requirements are for make-up.
As connection diameters increase, e.g., for diameters of 10" or
greater, the thread interference area increases until the point is
reached where the make-up torque required is not practical for
field operations.
As shown in FIG. 1, a prior art connection 10 includes a pin member
11 and a box member 12. Box member 12 has a tapered, internal,
generally dovetail-shaped thread structure 14 formed thereon and
adapted for engaging complementary tapered, external, generally
dovetail-shaped thread structure 15 formed on pin member 11 to
mechanically secure the box and pin members in a releasable
manner.
Internal thread 14 of box member 12 has stab flanks 18, load flanks
16, roots 20, and crests 24. The thread increases in width
progressively at a uniform rate in one direction substantially the
entire helical length of thread 14. External thread 15 of pin
member 11 has stab flanks 19, load flanks 17, roots 21, and crests
25. The thread increases in width progressively at a uniform rate
in the other direction substantially the entire helical length of
thread 15. The oppositely increasing thread widths and the taper of
threads 14 and 15, cause the complementary flanks, roots, and
crests of the respective threads to move into forcible engagement
during rotational make-up of the connection and form sealing
surfaces that resist the flow of fluids between the threads upon
rotational make-up of the connection.
The pin member 11 or the box member 12 defines the longitudinal
axis 13 of the made-up connection 10. The roots and crests of the
box and pin members are flat and parallel to the longitudinal axis
of the connection and have sufficient width to prevent any
permanent deformation of the threads when the connection is made
up.
SUMMARY OF THE INVENTION
A threaded pipe connection is disclosed that includes a box member
and a pin member. The box and pin members are formed in a two-step
configuration having a larger step and a smaller step. The box
member has a tapered, internal, generally dovetail-shaped thread
across both thread steps with stab flanks, load flanks, roots, and
crests. The pin member also has a tapered, external, generally
dovetail-shaped thread across both thread steps with stab flanks,
load flanks, roots, and crests. The internal thread of the box
member increases in width in one direction while the external
thread increases in width in the other direction so that the
complementary flanks of the respective threads move into engagement
during rotational make-up of the connection and form sealing
surfaces that resist the flow of fluids between the threads on at
least one step of the box and pin members upon rotational make-up
of the connection.
In accordance with one or more embodiments of the invention, a gap
may exist between the complementary stab flanks of one of the
thread steps of the box and pin members upon final make-up. A gap
may exist between the complementary load flanks of one of the
thread steps of the box and pin members upon final make-up. A gap
may exist in the stab flank and the load flank of one of the thread
steps upon final make-up. A gap may exist between the complementary
roots and crests of the box and pin members of one of the thread
steps upon final make-up. A gap may exist in one or more of the
complementary load flanks, stab flanks and roots and crests of the
box and pin members upon final make-up. The roots and crests of
both thread steps may come into contact during make up prior to
contact of both stab and load flanks of at least one thread step
upon final make-up. One of the wedge thread steps may be an
interference wedge thread step and the other may be a clearance
wedge thread step. A greater amount of root and crest interference
may occur on the interference wedge thread step than on the
clearance wedge thread step upon final make-up. Root and crest
interference may exist on the interference wedge thread step and
root and crest clearance may exist on the clearance wedge thread
step upon final make-up.
Advantages may include one or more of the following. By minimizing
thread interference area without sacrificing sealing or structural
integrity of the connector, it becomes practical for large diameter
connectors to be installed at much lower make up torque. Also, by
incorporating a two-step structure, high resistance to compression
and/or impact loading can be achieved, while sensitivity to the
torque restrictions of existing field make up equipment is
retained. Further, the two-step configuration of the invention will
reduce the amount of torque required to generate the contact stress
necessary for creating a seal, while still providing the necessary
threads for structural purposes. Other advantages and features will
become apparent from the following description including the
drawings and claims.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side view, partially in section, of a prior art tubular
joint;
FIG. 2 is a side view of a made-up pin member external thread
structure and a box member internal thread structure in accordance
with an embodiment of the invention;
FIG. 3 is an enlarged cross-section of a tubular joint at the point
of engagement between a pin member crest and a box member root in
the thick section of the box member in accordance with an
embodiment of the invention;
FIG. 4 is an enlarged cross section of a tubular joint at the point
of engagement between a pin member crest and a box member root in
the thin section of the box member in accordance with an embodiment
of the invention.
DETAILED DESCRIPTION
Referring to the drawings wherein like reference characters are
used for like parts throughout the several views, FIGS. 2, 3 and 4
illustrate a wedge-like thread connection or pipe joint, generally
referenced by numeral 110, in accordance with an embodiment of the
invention.
As shown in FIG. 2, internal thread 114 of box member 112 is formed
in a two-step wedge configuration providing two wedge thread steps
each with stab flanks 118, 218, load flanks 116, 216, roots 120,
220 and crests 124, 224. The thread increases in width
progressively at a uniform rate in one direction substantially the
entire helical length of thread 114. External thread 115 of pin
member 111 is formed in a two-step wedge configuration providing
two wedge thread steps each with stab flanks 119, 219, load flanks
117, 217, roots 121, 221, and crests 125, 225. The thread increases
in width progressively at a uniform rate in the other direction
substantially the entire helical length of thread 115. The
oppositely increasing thread widths and the taper of the threads
114 and 115 cause the complementary flanks, roots, and crests of
the respective threads to move into forcible engagement during
rotational make-up of the connection and form sealing surfaces that
resist the flow of fluids between the threads of one step while
leaving a clearance between the threads of the other step upon
rotational make-up of the connection.
As used herein, and as conventionally understood where tubular
joints are being connected in a vertical position such as when
making up a pipe string for lowering into a well bore, the term
"load flank" designates the side wall surface of a thread that
faces away from the outer end of the respective pin or box member
on which the thread is formed and supports the weight of the lower
tubular member hanging in the well bore. The term "stab flank"
designates that side wall surface of the thread that faces toward
the outer end of the respective pin or box member and supports the
weight of the upper tubular member during the initial make-up of
the joint.
FIGS. 3 and 4 are enlarged cross-sections, which, in one or more
embodiments, exist at positions 2 or 3 shown in FIG. 2. As shown in
FIG. 3, roots and crests on one step of pin member 111 are
dimensioned to eliminate radial clearance with complementary roots
and crests on one step of box member 112 during make-up of
connection 110. Also, stab flanks and load flanks on the one step
of pin member 111 are dimensioned to eliminate clearance between
complementary stab flanks and load flanks on the one step of box
member 112 during make-up of connection 110. For example, the roots
121 and crests 125 of the smaller step of pin member 111 may be
dimensioned to eliminate radial clearance with complementary roots
120 and crests 124 on the smaller step of box member 112 during
make-up of connection 110. Also, stab flanks 119 and load flanks
117 of the smaller step of pin member 111 may be dimensioned to
eliminate clearance between complementary stab flanks 118 and load
flanks 116 of box member 112 during make-up of connection 110. In
other words, thread roots 121 and thread crests 125 of pin member
111 come into interference contact with the corresponding thread
surfaces of box member 112, upon making the joint hand tight and
stab flanks 119 and load flanks 117 of pin member 111 come into
interference contact with the corresponding thread surfaces of box
member 112, upon making the joint power tight.
As shown in FIG. 4, roots and crests on the other step of pin
member 111 are dimensioned to leave radial clearance between
complementary roots and crests on the other step of box member 112
during make-up of connection 110. Also, the load flanks of the
other step of pin member 111 are dimensioned to leave clearance
between complementary load flanks on the other step of box member
112. For example, roots 221 and crests 225 on the larger step of
pin member 111 are dimensioned to leave radial clearance 250
between complementary roots 220 and crests 224 on the larger step
of box member 112 during make-up of connection 110. Also, load
flanks 217 on the larger step of pin member 111 are dimensioned to
leave clearance 250 between complementary load flanks 216 on the
larger step of box member 112 during make-up of connection 110. In
other words, thread roots 221 and thread crests 225 of pin member
111 remain in clearance from the corresponding thread surfaces of
box member 112, upon making the joint hand tight and load flanks
217 of pin member 111 remain in clearance from corresponding load
flanks 216 of box member 112 upon making the joint power tight.
Alternatively, the stab flanks 219 of pin member 111 may be
dimensioned to remain in clearance from complementary stab flanks
218 of box member 112 or both the stab flanks and load flanks of
pin member 111 remain in clearance from corresponding thread
structures on box member 112 upon make-up of the connection. Also,
though FIG. 4 shows clearance existing between both the roots and
crests and the load flanks, either could remain in clearance while
the other came into interference contact upon make-up of the
connection. Similarly, either of the roots and crests or the stab
flanks may remain in clearance while the other came into
interference contact upon make-up of the connection.
The disclosed configuration has many distinct advantages. The
two-step structure allows high resistance to compression and/or
impact loading, while retaining sensitivity to the torque
restrictions of existing field make up equipment. Further, the
two-step structure reduces the amount of torque required to
generate the contact stress necessary for creating a seal, while
still providing the necessary threads for structural purposes. The
disclosed configuration minimizes thread interference area without
sacrificing sealing or structural integrity of the connector. Since
connectors are able to be installed at a much lower make-up torque,
this invention is particularly advantageous in applications using
large diameter connectors, such as in surface casing.
It will be understood that certain features and subcombinations are
of utility and may be employed without reference to other features
and subcombinations. This is contemplated by and is within the
scope of the claims.
Because many possible embodiments may be made of the invention
without departing from the scope thereof, it is to be understood
that all matter herein set forth or shown in the accompanying
drawings is to be interpreted as illustrative and not in a limiting
sense.
While the present invention has been described with respect to a
limited number of preferred embodiments, those skilled in the art
will appreciate numerous modifications and variations therefrom.
The appended claims are intended to cover all such modifications
and variations which occur to one of ordinary skill in the art.
* * * * *